The present invention is related to compensation networks, and in particular to compensation networks utilized in conjunction with pressure sensors.
Pressure sensors are used in a variety of applications. A commonly employed type of pressure sensor is the piezo-resistive pressure sensor. These types of sensors typically include a silicon diaphragm incorporating an ion implanted piezo-resistive Wheatstone bridge. An applied pressure deflects the diaphragm and imbalances the bridge, producing differential output signal that is proportional to the change in resistance caused by the pressure. Piezo-resistive pressure sensors may be fabricated using either bulk silicon or silicon-on-insulator (SOI) wafers.
Changes in temperature cause changes in the resistance of the legs of the Wheatstone bridge, and can therefore lead to errors in the measured pressure. To accommodate changes in temperature, pressure sensors typically incorporate a resistive compensation network. The resistive compensation network operates by altering the electrical output signal at various temperatures by utilizing a resistor network. The resistor network changes its effective resistance value as a function of temperature to offset the change in output voltage of the Wheatstone bridge due to its temperature sensitivity. However, the resistive compensation network is ineffective if a temperature gradient exists between the Wheatstone bridge and the compensation network. For example, if the Wheatstone bridge is located in close proximity to a pressure medium with a temperature that differs from that of the ambient atmosphere surrounding the resistive compensation network hardware, the difference in temperature can lead to errors in the compensation provided.
In some situations in which accuracy must be maintained in the presence of a temperature gradient, a separate temperature sensing device (e.g., resistive temperature device) is located proximate to the pressure sensing element, and the output of the temperature sensing device is used by a digital device such as an on-board microprocessor or a separate electronic component with software to digitally compensate for temperature variation. However, this requires detailed characterization of the thermally-induced errors on the pressure sensor output during calibration of the pressure sensor, as well as separate wires out of the sensor assembly to conduct this signal to the electronic component, thus increasing cost and weight and reducing reliability.